This invention relates in general to machine operation control systems and, more specifically, to a method of and apparatus for monitoring and controlling the operation of preselected functions of individual machines in a plurality of machines.
More particularly, this invention relates to a digital communications system wherein specific operational functions of each machine in a series of machines are monitored and controlled from a single control subsystem or controller to assure individual machine performance in accordance with a predetermined program.
In all manufacturing and production operations, it is necessary to monitor and control the operation of the equipment used in the production and manufacturing processes. In certain applications this monitoring and controlling function is performed by the individual machine operator who may control more than one machine, depending upon the number of operations which must be monitored, and the frequency with which changes occur in these conditions and operations. However, the capabilities of an individual machine operator to control and monitor the equipment which is being utilized are limited. Therefore, it has been attempted to monitor the operation of these machines and to control their functioning through the use of a predetermined control program which monitors the various functions and conditions of a machine and controls the operation of the machine in response to these monitored conditions to insure satisfactory operation.
One attempt to provide such a solution to this problem has been the use of a controller which is programmed to couple predetermined control or command signals to the machines in the event a predetermined condition is detected thereby causing the command or control signal to be generated. In certain of these applications the detector or sensor which monitors the condition or operation, and the programmer or controller which generates the responding command signal, are each electrically coupled one to the other by wire pairs. This coupling or hard wiring necessitates a substantial expenditure of money for labor costs as well as the materials utilized in hard wiring the machine to the controller. Such a system obviously requires a controller to be in close proximity to the machine from a physical standpoint due to the large number of wire pair connections which must be made between the units.
Another attempt to provide a satisfactory solution to this problem has been the use of various multiplexing systems using a common transmission line or signal carrier between the machine and the controller wherein each of the individual functions of the machine which are monitored and the responding control signal generated to control proper machine operation are all transmitted by the common signal carrier. Such systems overcome the difficulties associated with hard wiring each monitor or sensor to its respective controller since they utilize a common transmission line, but they are limited as to the number of conditions which can be monitored within a given time frame.
In such a system each of the functions is sequentially monitored and the corresponding control signal coupled to the sensor. Such a system not only controls changes in the state of the sensed condition in response to the programmed control, but also insures that the correct state is maintained. These systems address each sensor and generate a command or control signal to the machine at every address regardless of a change of state in the controlled function or operation. Such a redundant system is satisfactory in applications where the number of monitored conditions is such that the entire system may be monitored or addressed within the limits of a predetermined maximum time frame. However, such systems are not satisfactory for use in monitoring a large number of inputs, or in smaller systems wherein the maximum time period within which a condition must be monitored or addressed is less than the time period required for the multiplexing system to complete its entire address cycle monitoring all terminals. In such systems if a monitored function were to change state immediately after the sensor has been addressed, the condition could not be changed until the next cycle -- after all of the other machine functions or operations had been addressed and the corresponding command signal transmitted to each receptor. In many applications such a time or cycle period is too great.
In monitoring or controlling machine operations where the "redundant" type of multiplexing systems, such as previously discussed, are not suitable due to the cycle time delay inherent in this system, a priority system has been utilized. In such systems the functions or conditions are arranged in priority of importance and sequentially addressed in synchronism, but no command signal is transmitted unless a change of state has been detected. The individual sensors or detectors of each group are addressed, and, upon a change being detected, a command signal is generated to correct or change the condition or function. At the end of the transmission cycle to that particular receptor, the entire functions or controls series are again addressed beginning with the highest priority function or control, and the addressing of the entire cycle restarted to continue until a change is detected. Such a system requires that each of the functions or controls which are to be monitored must be ranked according to their importance, and presents the problem that the lower ranked priorities may never be monitored.
In another type of priority system the monitored functions or controls are electrically coupled into two groups. The first group comprises a small number of high priority terminals and the second group contains the remaining monitored terminals. The high priority group is sequentially addressed and a command signal is generated for each of the functions in this group in the manner previously described with reference to the "redundant" type of multiplexing system. The remaining functions or controls are addressed, but no command signal is generated unless the sensor for these controls or functions has indicated that a change or a command signal is necessary.
Another type of priority multiplexing system utilizes a random access memory and a two-speed addressing rate which addresses all of the monitored conditions to determine a change of state requiring a response, but only transmits data through the common signal carrier upon the occurrence of a monitored event or the sensing that a response-requiring change has occured. While this system eliminates the problems incurred by delay time due to the transmission of command signals to functions or controls which do not need a command signal for proper operation, they require further and more sophisticated electronics in that the individual monitors or detectors must be provided with additional informational data identifying the receptor to insure correct correspondence between the function monitored and the command signal generated in response since there cannot be any synchronization between the controller and the receiver. The resulting random transmission of control or command signals to the monitored receptors must, therefore, be accompanied by informational data which correlates the particular function or control which is being monitored and the command signal directed to change the state of a particular operation or function to insure that the command signal is coupled to the appropriate receptor. Such a system requires highly sophisticated electronics and is, therefore, expensive.
With all of the various types of priority systems which have been utilized, each of these systems is burdened with the inherent problem that, in order to give certain machine functions priority, other monitored functions must of necessity yield to these priorities. Therefore, the secondary or non-priority functions may become critical through lack of a command response being directed to the receiver because of the continued utilization of the common signal carrier or transmission line by the higher priority informational data. Even though the various multiplexing systems discussed above are of benefit in minimizing the expenses incurred in monitoring and controlling the operations of a machine, such systems inherently present further problems which must be minimized in order to obtain an economical and commercially acceptable system.